Brilliant Infrared Light Sources for Micro-Ellipsometric Studies of Organic Thin Films

Micro-ellipsometric studies in the infrared and THz spectral range are of increasing interest in particular for the determination of the optical constants of organic films and multilayers as in these cases the composition, thickness or roughness often vary on micro- and mesoscopic length scales. In cases where the aforementioned properties change across the probed spot, the degree of polarization of the reflected beam is deteriorated and sophisticated models have to be employed to derive the optical constants or other parameters from the determined ellipsometric angles. The achievable spot size in an ellipsometric set-up is now limited by the necessity to perform a specular reflectance measurement with a reasonably defined angle. In the optimal case the infrared radiation can be focused to near diffraction limited spot sizes with opening angles in the incoming beam of less than 7°. In other words such an experiment turns out to be limited by a source property that is typically called brilliance or brightness and makes the technique particularly suited for the use of accelerator based infrared sources such as 3rd generation synchrotron storage rings. The current status of such activities worldwide will be reviewed and discussed on the example of different pilot experiments and an outlook on future developments will be given.